1. Field of the Invention
The present invention relates to a Radio Frequency (RF) transmitter suitable for use in a wireless transmission apparatus that transmits a high-power radio signal, such as a wireless communication Base Station (BS), and a signal amplification method therefor.
2. Description of the Related Art
FIG. 1 is an exemplary block diagram of a conventional RF transmitter. Referring to FIG. 1, the conventional RF transmitter includes an Intermediate Frequency (IF) signal source 10 for generating an IF signal in a predetermined frequency band, for example, a 100-MHz modulated IF signal, a first amplifier 11 for amplifying the IF signal received from the IF signal source 10 with a predetermined gain, and a first Band Pass Filter (BPF) 12 for filtering the amplified signal received from the first amplifier 11 in a corresponding IF signal band.
The conventional RF transmitter further includes a Local Oscillator (LO) 18 for generating a signal in a predetermined high frequency band, for example, a 2-GHz high frequency signal and a second amplifier 17 for amplifying the high frequency signal generated from the LO 18 with a predetermined gain.
In addition, the conventional RF transmitter includes a mixer (e.g. a modulator) 13 for generating a signal of an intended frequency by mixing the signals received from the first BPF 12 and the second amplifier 17. The mixer 13 may be configured in one of known mixer technologies. The mixed (converted) signal is provided to a power amplifier 15 via a second BPF 14 for filtering the frequency band of a local oscillation signal.
The transmission-level power amplifier 15 may be configured as a linear high-power amplifier, for amplifying the signal received from the second BPF 14 to an intended transmission level. The power amplifier 15 is driven by a DC power source 152. The signal output from the power amplifier 125 is provided to a third BPF 16. The third BPF 16 generates a final RF signal by filtering a transmission band.
One or more of the first, second and third BPFs 12, 14 and 16 may be omitted in a real circuit configuration of the RF transmitter. The first amplifier 11 and the second amplifier 17 are used to compensate for path loss in transmission lines and signal processing devices that a signal generated from the IF signal source 10 or the LO 18 passes through. In some cases (on the whole), the first and second amplifiers 11 and 17 are not needed.
The power amplifier 15, which amplifies a signal to a transmission level, should be configured to be a high-power amplifier. Considering a Peak-to-Average Power Ratio (PAPR) component that may be included in the IF signal of the IF signal source 10 and Inter-Modulation Distortion (IMD) caused by mixing the IF signal with the local oscillation signal in the mixer 13, the power amplifier 15 should be configured as a linear amplifier, especially a power amplifier having higher performance than needed in theory. For instance, even when a 48-dBm output is required in theory, a power amplifier having a very high performance of 56 dBM is used.